Modern Warfare 4 is reportedly in development, according to a supposed conversation that happened between Captain Price's voice actor Bill Murray and a game blogger who found himself seated beside the man on a plane.
As the story goes, a game enthusiast and blogger wound up beside Murray on an airplane from Bondrum to London (he included a photo). During the trip, he asked the actor all sorts of questions, and while most of it isn't stuff he can repeat, he quoted Murray confirming the following:
"On Monday I am off to meet Infinity Ward about the next game, Modern Warfare 4. I'm doing work on the sequel to Modern Warfare 3, it carries straight on and I only ever appear in the Modern Warfare games…"
Certainly hearsay isn't always the best evidence, but it's not like we're all shocked by there being another Modern Warfare. Those who finished the last Modern Warfare campaign may have debated whether the conclusion was final, but hey, it's Call of Duty.
Black Ops 2 will be out on November 13, and we typically see Treyarch trading off with Infinity Ward on a yearly basis. Given this pattern, the timing of a Modern Warfare 4 isn't all that off.